Sil-X stage balls are partially filled with liquid silicon. The liquid centre gives the ball a nice weight and a low centre of gravity making arm/body rolls and stalls easier than standard stage balls. Foot and neck stalls and head balances are also facilitated by the stability of these balls. The 78mm Sil X's are a great middle ground; they are big enough to be good for body rolling and small enough to be used as stable juggling balls. The SilX ball still has a little bit of squish to it, making catches nice and comfortable. Warning: If stored incorrectly these balls can become misshapen. Warning: The white balls should be stored separately as they can take on the colour of other balls/objects they comes in to contact with. Weight: 150g